Physical Attraction

The Mysteries of Magnetism

Joachim Stöhr

SSRL/SLAC

Magnetism and Humans

Magnetic Attraction

“Animal Magnetism” –Mesmerizing –

Magnetic Healing

From myth

to sc

ience …

..

Magnetic Objects

Magnetic Devices

Overview of Talk

• A historical perspective … the spin on magnetism …

• Magnetism today… the hi-tech society

• A Glimpse of the Future……ultra-small, ultra-fast

A historical perspective

first described “magnetism” as the attraction of iron by ``lodestone“- lodestone is the naturally occurring mineral magnetite Fe3O4

Thales of Miletus (Greek, ~ 634 - 546 BC)

Legend: Shepherd by the name of Magnés found that his iron tipped cane was attracted to rocks

The term “magnetism”

More probable:Name comes from city of Magnesia (modern Turkey) surrounded by magnetic rock deposits

Si Nan - the south governor China, ca. 200 BC

bronze plate

south

direction pointers likely used for feng shui - the method of achieving harmony with the forces of nature by properly aligning buildings and placing of objects.

magnetic lodestone spoon

In 1600 William Gilbert published his book“De Magnete“ - “About the Magnet“

he explained that compass needle points north-south because earth is magnetic

William Gilbert (England, 1544-1603)

Earth is magnetic - compass follows its field

Naval navigation:China in late 11th or early 12th century compass became known in Europe sometime later in the 12th century

Earth field mostly from electric currents in the liquid iron outer core

Field changes direction about every 500,000 years

Franz Anton Mesmer theorized that "animal magnetism" accounted forhis ability to heal.

(Germany/Austria 1734-1815)

Around 1800: mythical magnetism

Franz Anton Mesmer

Mesmerizing a patient

“The mystery of magnetism, explain that to me ! No greater mystery, except love and hate.”

Natural Philosophy:

two opposites make a “whole”love – hateblack – white north – southplus – minus

magnetism is fundamental, it is just there – it does not need to be explained

Johann Wolfgang von Goethe (Germany, 1749-1832)

Around 1800:

…contains important modern element: there are no magnetic monopoles!

(Denmark, 1777-1851) Hans Christian Oersted

1819 – a breakthrough discovery

1831: The foundation of the industrial society

Electric generator: motion electricity

(England, 1791 – 1867)

Michael Faraday

Electric motor: electricity motion

Fuel - burns - hot gases - turbine

US electricity retail sales:

$ 250 billion/year ($ 0.25 trillion)

Electricity is big $$$$$$$

Nuclear - heats water - steam - turbine

Hydro-electric - water drives turbine

About half of the US energy is consumed as electricity

Total Gross Domestic Product (trillions of $)

1. United States 10.92. Japan 4.33. Germany 2.44. United Kingdom 1.85. France 1.7 6. Italy 1.57. China 1.4

1845: Magnetism and light – a connection !

1791 - 1867

again…

Michael Faraday

Light must have a magnetic component

(Scotland, 1831 – 1879)

1864: Maxwell’s equations: coupling of electric and magnetic phenomena

Light is an electromagnetic wave

Ludwig Boltzmann (Germany,1844-1906)

“Was it a god who wrote these symbols…unveiling the forces of nature?”

James Clerk Maxwell

only wavelength is different

The electro-magnetic spectrum: “wireless waves at the speed of light”

Visible light

It is hard to imagine our society without wireless technology !

1921-1928: Getting to the origin of magnetism 7 years that changed physics and magnetism

• The concept of the spin (Pauli, Uhlenbeck & Goudsmit, Dirac)

• Quantum theory (Heisenberg, Schrödinger, Dirac)

• Magnetic exchange interaction in materials (Heisenberg)

The mystery of spin: when measured, it is always along a “quantization axis” – “up” or “down”

The inside of magnets: origin of magnetism

magnet = arrangement of atoms with aligned spins

Magnetism today……

the high-tech society…

……beyond electricity and wireless

The spin on electronics: magnetic devices in computers

“0” and “1” bits = small magnetic areas with opposite magnetization direction

“chip - RAM”

“disk”

Magnetic recording technology

Courtesy of Jan Thiele, Hitachi

stack of 50 giant discs, 24" diameter

total 4.4 MB - $35,000/year rent

Today:

200 GB = 200, 000 MB - $ 90

IBM RAMAC 1956:

The Data Storage Industry $53 billion/year worldwide revenues

10,000 songs

1 song

Magnetic recording: Small and fast !

1 mile/hour

1000 miles/hour

Incredibly small bits – incredible writing and reading speeds

The invisible ultra-small world

understand size limits -- no stable bits--

X-ray images … then and now

1895W. Röntgen, Würzburg

1993SSRL/SLAC

X-rays have come a long way……

10,000 times smaller

01 “bits”

A Glimpse of the Future……

exploring ultrafast time scales

….is there a data storage speed limit ?

With this method we cannot explore faster switching today …. is there a speed limit ????

Present switching pulses are generated by current flow through wires

most advanced technology: 100 picosecond (10 billionth of a second) current pulsesmagnetic recording works fine

“Oersted fields”

The ultra-fast world

How can we explore this void?

An electro-magnetic brainstorm

Create an artificial “lightning bolt”and use it to switch a magnetic sample !

(Prof. ETH Zürich, Switzerland)

Creation of large, ultrafast magnetic fields

Conventional method

- t

oo slow

Artificial “lightning bolt” – an electron accelerator

sample

Magnetic writing with SLAC beam

The Speed Limit of Magnetic Switching

tpulse= 3 ps tpulse= 100 fs

30 times faster than conventional -- switching still works reliably --

There is a speed limit!

90 m90 m

01 01 1

1000 times faster than conventional -- switching is not reliable --

.. but we don’t understand why!

The magnetic recording limits: size and speed

size speed

factor < 1000 to go

factor 30 x 150 ~ 5000 to go

Linac Coherent Light Source – LCLS the first x-ray laser in the world

Near Hall

Far Hall

FEL Center

to come in 2008

The future: seeing the invisible at ultrafast speeds

In Summary…..

Magnetism ….

• is an old phenomenon and topic

• has many important practical applications navigation … electricity … wireless communication… medical imaging

• underlies modern data storage technology may be used in future for computer memory and “quantum computing”

• remains an exciting research topic

... the mystery of magnetism continues...

Acknowledgements

Ann Mueller, SSRL

Science website:http://www.howstuffworks.com

My research group:http://www-ssrl.slac.stanford.edu/stohr

http://www-ssrl.slac.stanford.edu/stohrgroup